1 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved. Distributed Systems Architectures

1 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved.

DistributedSystems

ArchitecturesIS301 – Software Engineering

Lecture # 15 – 2004-10-04M. E. Kabay, PhD, CISSP

Assoc. Prof. Information AssuranceDivision of Business & Management, Norwich University

mailto:[email protected] V: 802.479.7937

mailto:[email protected]


Objectives

To explain the advantages and disadvantages of different distributed systems architectures

To discuss client-server and distributed object architectures

To describe object request brokers and the principles underlying the CORBA standards

To introduce peer-to-peer and service-oriented architectures as new models of distributed computing.


Topics covered

Multiprocessor architectures Client-server architecturesDistributed object architectures Inter-organizational computing

Today we will use 27 of Prof. Sommerville’s

slides in class


Distributed systems

Virtually all large computer-based systems are now distributed systems.

Information processing is distributed over several computers rather than confined to a single machine.

Distributed software engineering is therefore very important for enterprise computing systems.


System types

Personal systems that are not distributed and that are designed to run on a personal computer or workstation.

Embedded systems that run on a single processor or on an integrated group of processors.

Distributed systems where the system software runs on a loosely integrated group of cooperating processors linked by a network.


Distributed system characteristics

Resource sharingSharing of hardware and software resources.

OpennessUse of equipment and software from different

vendors.Concurrency

Concurrent processing to enhance performance.Scalability

Increased throughput by adding new resources.Fault tolerance

The ability to continue in operation after a fault has occurred.


Distributed system disadvantages

ComplexityTypically, distributed systems are more

complex than centralized systems.Security

More susceptible to external attack.Manageability

More effort required for system management.

UnpredictabilityUnpredictable responses depending on the

system organization and network load.


Distributed systems architectures

Client-server architecturesDistributed services which are called on by

clients. Servers that provide services are treated differently from clients that use services.

Distributed object architecturesNo distinction between clients and servers.

Any object on the system may provide and use services from other objects.


Middleware

Software that manages and supports the different components of a distributed system. In essence, it sits in the middle of the system.

Middleware is usually off-the-shelf rather than specially written software.

ExamplesTransaction processing monitors;Data converters;Communication controllers.


Multiprocessor architectures

Simplest distributed system model.System composed of multiple processes

which may (but need not) execute on different processors.

Architectural model of many large real-time systems.

Distribution of process to processor may be pre-ordered or may be under the control of a dispatcher.


A multiprocessor traffic control system

Traffic lights

Lightcontrolprocess

Traffic light controlprocessor

Traffic flowprocessor

Operator consolesTraffic flow sensors and

cameras

Sensorprocessor

Sensorcontrolprocess

Displayprocess


Client-server architectures

The application is modeled as a set of services that are provided by servers and a set of clients that use these services.

Clients know of servers but servers need not know of clients.

Clients and servers are logical processes The mapping of processors to processes is

not necessarily 1 : 1.


A client-server system

s1

s2 s3

s4c1

c2 c3 c4

c5

c6c7 c8

c9

c10

c11

c12

Client process

Server process


Computers in a C/S network

Network

SC1SC2

CC1 CC2 CC3

CC5 CC6CC4

Servercomputer

Clientcomputer

s1, s2 s3, s4

c5, c6, c7

c1 c2 c3, c4

c8, c9 c10, c11, c12


Application layers

Presentation layer

Application processinglayer

Data managementlayer


Thin and fat clients

Thin-clientmodel

Fat-clientmodel Client

Client

Server

Data managementApplication processing

Presentation

Server

Data management

PresentationApplication processing


A client-server ATM system

Account server

Customeraccountdatabase

Tele-processingmonitor

ATM

ATM

ATM

ATM


A 3-tier C/S architecture

Client

Server

Datamanagement

PresentationServer

Applicationprocessing


An internet banking system

Database server

Customeraccountdatabase

Web serverClient

Client

Account serviceprovision

SQLSQL query

HTTP interaction

Client

Client


Distributed object architecture

Object request broker

o1 o2 o3 o4

o5 o6

S (o1) S (o2) S (o3) S (o4)

S (o5) S (o6)


A data mining system

Database 1

Database 2

Database 3

Integrator 1

Integrator 2

Visualiser

Display

Report gen.


CORBA application structure

CORBA services

Domainfacilities

Horizontal CORBAfacilities

Applicationobjects

Object request broker


ORB-based object communications

o1 o2

S (o1) S (o2)

IDLstub

IDLskeleton

Object Request Broker


Inter-ORB communications

o1 o2

S (o1) S (o2)

IDLstub

IDLskeleton


o3 o4

S (o3) S (o4)

IDLstub

IDLskeleton


Network


Decentralized p2p architecture

n1

n2 n3

n4

n5

n6

n7

n8

n9 n10 n11

n12

n13

n13


Semi-centralized p2p architecture

Discoveryserver

n1

n2

n3

n4

n5

n6


Web services

Serviceregistry

Servicerequestor

Serviceprovider

Publish

Bind

Find

service


Automotive system

User interface

Locator

Discovers carposition

Weatherinfo

Receives requestfrom user

Receiver

Receivesinformation stream

from services

Transmitter

Sends position andinformation request

to services

Radio

Translates digitalinfo stream toradio signal

In-car software system

Mobile Info Service

Facilitiesinfo

Translator

Roadlocator

Trafficinfo

Collates information

Road traffic info

commandgps coord

gpscoord gps coordgps coord

Languageinfo

Infostream

Service discovery

Finds availableservices


Homework

RequiredBy 11 Oct 2004For 20 points, answer in detail

12.3, 12.8 (@10) [use computer-drawn diagrams for these two]

For 5 points, answer in detail 12.5Optional

By 18 Oct 2004For a maximum of 8 additional points,

answer any or all of12.1, 12.2, 12.4, 12.6 (@2)

Names etc. on upper

right, please


DISCUSSION

Documents

1 Note content copyright © 2004 Ian Sommerville. NU-specific content copyright © 2004 M. E. Kabay. All rights reserved. Distributed Systems Architectures